1. Field of the Invention
This invention relates in general to tack spraying apparatus, and more particularly to motorized tack spraying vehicles and to spray nozzles utilized in tack spraying apparatus.
2. Prior Art
“Tack” is commonly known in the art to encompass asphaltic emulsions, liquid asphalt, or a variety of other substances that are coated onto a surface to be paved prior to distributing and compacting the hot mix asphalt (HMA) into a mat to bind the HMA to the underlying surface. Typically, the emulsion comprises liquid asphalt, water and an emulsifying agent. In more current formulations, the emulsion can also include polymers, such as SBS and SBR polymers.
Tack is typically applied, just prior to a paving operation, by being sprayed onto the surface to be paved from a spray bar extending transversely over the surface. A tack truck operated independently of the paving machine is normally used for this purpose. The typical tack truck includes a self-propelled chassis on which are mounted a tack storage tank and a tack spray assembly. The truck travels in front of the paving machine while coating the surface to be paved with a layer of tack. The truck travels at 5 to 10 miles per hour, considerably faster than the 20 to 40 feet per minute operational speed of the paving machine, and hence must periodically stop to wait for the paving machine and associated components of the paving system to catch up with the truck. Examples of such tack application systems are disclosed in U.S. Pat. No. 4,828,429 to Kirchner et al; U.S. Pat. No. 4,684,289 to Gnesa, and U.S. Pat. No. 4,793,731 to Gnesa. These systems have various drawbacks such as the paving equipment becoming covered with the tack, the accidental spraying of tack on vehicles passing in an adjacent lane of the road being paved. Solutions to some of these problems have been addressed by incorporating the tack storage tank and tack spraying equipment into the paving machine. Examples of such systems are seen in U.S. Pat. No. 5,851,085 to Campbell, U.S. Pat. No. 5,131,788 to Hulicsko, and U.S. Pat. No. 4,944,632 to Dillingham.
However, serious problems remain in providing a simple tack application system that can uniformly distribute the tack with downtime to fix clogged spray nozzles and transfer lines. This problem has become more acute with the increasing use of polymer material in the tack emulsion. These polymers have a greater tendency to form relatively large globules if the tack becomes cool or after prolonged storage. When this occurs these globules can enter and clog the transfer lines or spray nozzles preventing further dispersion of tack, or cause uneven distribution or application on the road surface.
Another remaining problem is the costs of all the various pieces of equipment involved in applying emulsions on both hot-mix overlay and soil cement applications. Reduction in the number of pieces of equipment and associated costs would be a desirable advance in the art.
Still other problems in the art include the ability to measure the amount of tack within the storage tank, as well as the tack output on a continual basis.